1. Field of the Invention
The present invention relates to an idle revolution speed control apparatus for an internal combustion engine to be mounted on an automobile.
2. Discussion of Background
There has been known an idle revolution speed control apparatus which prevents a rapid change of an engine revolution speed or stabilizes the revolution speed by detecting load conditions which affect the operation of the engine, and controls an intake air quantity with use of an actuator which changes the intake air quantity to the engine depending on the load conditions.
Various electric loads affect on the operation of the engine. Accordingly, an automobile is provided with a generator driven by the engine and a generator control device which controls a voltage and a current generated from the generator.
An electricity generating unit constituted by the generator and the generator control device forms a relatively large load to the engine having a relatively small output capacity, especially, when the engine is in an idle state. It is found that when a large electric load such as head lamps is actuated, the electricity generating unit constitutes a substantial load to the engine as the electric quantity increases.
In the conventional idle revolution speed control apparatus, an idle revolution speed control was effected without considering an amount of load increase caused by the electricity generating unit. As another conventional idle revolution speed control apparatus, an electric load signal representing a load such as a head lamps was inputted to the generator control device and a predetermined amount of intake air was introduced into the engine on the basis of the information of the electric load signal in order to avoid the reduction of the idle revolution speed with an increased load of the electricity generating unit when the load was applied to the engine.
In the conventional idle revolution speed control apparatus having an electric load correcting function, there was a problem that the idle revolution speed of the engine was reduced with increase of load to the engine due to the generator when the electric load was applied to the engine. This causes vibrations in the engine speed, which results in drivability deterioration or an engine stop.
In the conventional idle revolution speed control apparatus having the electric load correcting function, there was the following problem. Since it was necessary for such apparatus to have a control device for detecting an electric load and a wiring for the control device, the manufacturing cost of the idle revolution speed control apparatus increased even though the idle revolution speed of the engine to which an electric load was applied, was stabilized in comparison with the control apparatus without having the electric load correcting function.